Several security mechanisms are used in the circuit to ensure that the motor-compressor is protected. The most common security management;
Director-safety switch.
Low pressure safety cut-out.
Oil pressure safety cut-out.
One of the most harmful things that can happen to the sealing system to have high head (condensing) pressure. These high pressures temperature increase of oil gases and moving past the discharge valve of the compressor. This can lead to oil and refrigerant breakdown. This condition is aggravated if some of the water and the mud there. Carbon acids and sludge can be formed.
It is important to turn off the system before these dangerous temperature has reached a high pressure safety cut-out is often used for this purpose. If the pressure exceeds a preset value, the current value of the motor will be switched off. Thus, the engine will stop.
Several conditions may lead to such a control:
Lack of proper circulation of air through the condenser,
The lack of flow of water through a water-cooled condenser.
Low pressure switch can also be used as a protective device. Cooling compressor motor depends on the amount and temperature of the suction vapor. If the vapour pressure is too low (system low refrigerant flow or limited), the motor-compressor can overheat and ass. Low-pressure safety control will stop the motor-compressor, before he damaged, circuit diagram on the low side or suction pressure control is shown in Fig. 8-53.
Some use a larger units safety control device connected to the system of lubrication of the compressor. These switched off if the oil pressure drops. They also disable if the oil pressure drops below the set of safe pressure above the low pressure side. Design similar to the low pressure control, but, as a rule, fixed or unregulated differential. This control has one connection for the oil pump and one connection on the side of low pressure.
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